Heat fixing apparatus for fusible material



March 3, 1970 R. MOSER 3,498,596

HEAT FIXING APPARATUS FOR FUSIBLE MATERIAL Filed May 24. 1968 3 Sheets-Sheet 1 INVENTOR. RABI N MOS ER BY 6- 4. 0M

ATTORNEYS March 3, 1970 R. MOSER 3,498,596

HEAT FIXING APPARATUS FOR FUSIBLE MATERIAL Filed May 24. 1968 3 Sheets-Sheet 2 FIG. 2

INVENTOR. RABIN MOSER A T TOR/VE VS March 3, 1970 R. MOSER 3,498,596

HEAT FIXING APPARATUS FOR FUSIBLE MATERIAL Filed May 24. 1968 3 Sheets-Sheet 3 INVENTOR. RABI N MOSE R United States Patent 3,498,596 HEAT FIXING APPARATUS FOR FUSIBLE MATERIAL Rabin Moser, Fairport, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed May 24, 1968, Ser. No. 731,965 Int. Cl. F27b 9/06, 9/14; F27d 3/00 US. Cl. 2636 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to heat fixing systems, and particularly, to improvements in fuser apparatus for particulate material such as resinous toner particles, that are used in electrostatic automatic copiers/reproducers capable of high speed operation.

It has been recognized that one of the preferred methods of applying heat for fusing the powder image to paper is to bring the powder image into direct contact with a hot surface, such as a heated roller. However, in order to produce fused images elfectively and efliciently, it has been necessary to utilize relatively large and structurally dense fuser rollers which consume large amounts of heat in order to overcome heat losses effected by the roller supporting structures. Heater elements for these roller fusers are generally supported interiorly of one of the rollers which have high temperature gradients needing a relatively large power supply was needed to overcome heat losses as well as for fusing purposes. With the requirement for high fuser heater element temperatures comes the need to provide elaborate temperature controls to insure against over-temperature and equipment protection. For some application in offset prevention, a tetrafluoroethylene resin based material, such as, Teflon is utilized. This material has the physical characteristic of being substantially adhesive to some tackified xerographic developing materials. However, its release or adhesive characteristic to some developing material, while in a tackified condition is not completely adequate for many of the more desirable developing particles at their fusing temperatures. To aid in offset prevention, a fusing roller coated with Teflon material is usually coated with a thin film of silicone oil by means of an oil applicator wick. This arrangement requires an oil reservoir and wick supply and the cleaning thereof. There are other heat fixing devices not particularly suited for high speed copying/ duplication, such as, coiled radiant element heaters with reflectors. These radiant element heaters with reflectors and other types such as the recirculating heated air type have the disadvantage of dissipating a large quantity of heat into the machine enclosure in which they are used, heat transfer to the powder image is inefficient, and for the case of the coiled heater element they present a safety hazard because of the exposed element.

It is, therefore, the principal object of this invention to improve the construction of a direct contact fusing devicefor toner images which will require a minimum of heat to accomplish the rapid fusing of toner images.

This and other objects of the invention are attained "ice by means of a direct contact fusing device in which the toner image is fused by forwarding the sheet or web of paper bearing toner images between two rollers, one of which is heated exteriorly and being provided with a thin blanket of an insulating material, such as silicone rubber and a coating of room temperature vulcanizing silicone rubber with better release properties as an outer coating of the roller.

For a better understanding of the invention, as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings, wherein:

FIG. 1 illustrates schematically a xerographic reproducing apparatus adapted for high speed automatic operation, and incorporating a roller heat fuser constructed in accordance with the invention;

FIG. 2 is a plane view, partly in section of the fuser apparatus shown in FIG. 1;

' FIG. 3 is an elevational view of the fuser assembly as seen from the rear of the machine;

FIG. 4 is an end view of the fuser assembly as seen from the front of the machine;

FIG. 5 is a sectional view taken along the line 5--5 in FIG. 3; and

FIG. 6 is an enlarged fragmentary sectional view of the peripheries of the rollers utilized in the fuser apparatus.

For a general understanding of the illustrated copier/ reproduction machine, in which the invention may be incorporated, reference is had to FIG. 1 in which the various system components for the machine are schematically illustrated. As in all electrostatic systems such as a xerographic machine of the type illustrated, a light image of a document to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged developing material to form a xerographic powder image, corresponding to the latent image on the plate surface. The powder image is then electrostatically transferred to a support surface to which it is fused by a fusing device whereby the powder image is caused permanent to adhere to the support surface.

In the illustrated machine, an original D to be copied is placed upon a transparent support platen P fixedly arranged in an illumination assembly generally indicated by the reference numeral 10, arranged at the left end of the machine. The image rays are projected by means of an optical system for exposing the photosensitive surface of a xerographic plate in the form of a flexible photoconductive belt arranged on a belt assembly generally indicated by the reference numeral 11.

The photoconductive belt assembly 111 is slidably mounted upon the frame of the machine and is adapted to drive the selenium belt 12 in the direction of the arrow at a constant rate. During this movement of the belt, the light image of the original on the platen is flashed upon the xerographic surface of the belt. The flash exposure of the belt surface to the light image discharges the photoconductive layer in the areas struck by light, whereby there remains on the belt a latent electrostatic image in image configuration corresponding to the light image projected from the original on the supporting platen. As the belt surface continues its movement, the electrostatic image passes through a developing station B in which there is positioned a developer assembly generally indicated by the reference numeral 14. The developer assembly 14 deposits developing material to the upper part of the belt assembly 11 whereat the material is directed to cascade down over the upwardly inclined selenium belt 12 in order to provide development of the electrostatic image. As the developing material is cascaded over the xer-ographic plate, toner particles in the development material are deposited on the belt surface to form powder images.

The developer electrostatic image is transported by the belt to a transfer station -C whereat a sheet of copy paper is moved at a speed in synchronism with the moving belt in order to accomplish transfer of the developed image. There is provided at this station a sheet transport mechanism generally indicated at 16 adapted to transport sheets of paper from a paper handling mechanism generally indicated by the reference numeral 18 to the developed image on the belt at the station C.

After the sheet is stripped from the belt 12, it is conveyed to a fuser apparatus generally indicated by the reference numeral 20 whereat the developed and transferred xerographic powder image on the sheet material is permanently affixed thereto. After fusing, the finished copy is discharged from the apparatus by a belt conveyor 21 to a suitable point for collection externally of the apparatus.

Suitable drive means may be arranged to drive the selenium belt I12 in conjunction with timed fiash exposure of an original to be copied, to effect conveying and cascade of toner material, to separate and feed sheets of paper and to transport the same across the transfer station C and to convey the sheet of paper through the fuser assembly in timed sequence to produce copies of the original.

It is believed that the foregoing description is suflicient for the purposes of this application to show the general operation of an electrostatic copier using an illumination system constructed in accordance with the invention. For further details concerning the specific construction of the elestrostatic copier, reference is made to copending application Ser. No. 731,934 filed concurrently herewith, on May 24, 1968 in the name of Hewes et a l.

As shown in FIGS. 2 to 6, the fuser apparatus 20 is of the pressure-roller heat type and includes a frame for supporting a lower roller of the fuser apparatus, the frame including two spaced apart end plates 25, 26 supported in parallel relationship vertically by a base plate 27 secured to the main frame for the machine utilizing the fuser assembly. The frame is also provided with a rear brace 28 secured to the rear edges of each of the plates 25, 26 and a brace 30 secured between the end plates at the forward section thereof.

Direct contact fusing of a powder image on a sheet of paper support material is achieved by forwarding a sheet bearing the powder image to be fused between a heated lower roller, generally designated 30, rotating into and under pressure during a fusing operation with an upper roller 31. The sheet of support material carrying the unfused toner images is directed between the nip of the rollers 30, 31 by means of guide rods 32 extending between the transport system 16 and the adjacent end of the fuser apparatus 20.

As shown in FIGS. 2, and 6, the lower roller 30 comprises a supporting thin wall, metallic cylinder 33 closed at both ends by caps 34 made of heat insulating material. Each of the caps 34 in turn is secured upon a shaft 35 which supports the roller 30 for rotation within the fuser assembly 20. The ends of the shaft 35 are rotatably mounted by bearings 36 upon the end plates 25, 26.

Surrounding the metallic cylinder 33 of the roller 30 is a heat insulating, silicone rubber blanket 37 having a radial thickness of suflicient dimension and, with some pliableness, to permit indentation thereof when the upper roller 31 is in pressure relationship therwith. Any other high temperature, and thermal insulation material may be utilized for the blanket 37, such as glass, cloth or other ceramic forms which can be made slightly pliable, as well as high temperature resisting foams or sealed elastomeric sleeves which can be made highly pliable. The blanket 37 in turn is coated with a thin coating 38 of a room temperature vulcanizing compound, such as the Dow Corning Release Agent 236, produced by the Dow Corning Company. Since this material as such is highly reflective, it is preferred that it be mixed by approximately 5% by weight with the Dow Corning RTV 73-5 Sealant Adhesive which diminishes the reflective quality of the basic material without affecting the release quality thereof and thereby greatly enhancing the heat absorbing ability of the coating 38 with the blanket 37. Diminishing the reflective quality can be accomplished also by mixing carbon b ack or dyes with the release agent. The coating 38 serves as a release agent for the resinous toner particles that are brought into contact with the coating during fusing operation and, the blanket 37 serves as a heat barrier relative to the supporting structure for the roller 30. Another material that has exhibited suitable release characteristics for the newly produced low temperature melting toner particles has been the silicone rubber material sold by Dow Chemical Corporation under their trademark Silastic RV 501. Any other material may be utilized instead of a room temperature vulcanizing compound providing that its release properties remain effective at or above the fusing temperature of the toner particles being fixed to a sheet of support material.

The upper roller 31 comprises a metallic cylinder 40 supported on a shaft 41 by means of caps 42 secured to the shaft and to the interior surface of each end of the roller. A coating 43 of insulating adhesive material such as Teflon surrounds the cylinder 40 and should be of sufficient hardness to produce indentation of the materials 37, 38 on the roller 30 when in pressure contact. The shaft 41 is mounted at each end in suitable bearings mounted on a pair of plates 44, 45 pivotally mounted upon end plates 25, 26 respectively Each of the plates 44, 45 is mounted for limited pivoting movement relative to a common axis by means of a pivot pin 46 secured to the end plate 25 and rotatably supporting the plate 44 and a second pivot pin 47 secured to the end plate 26 and pivotally supporting the plate 45. As the plates 44, 45 are pivoted in the same direction about the axis defined by the pins 46, 47 the upper roller 31 is moved relative to the lower heated roller 30.

Pivotal movement of the upper roller support plates 44, 45 is accomplished by means of an air pressure actuated drive mechanism arranged to impart pivotal movement to the plates in either direction to raise or lower the upper roller 31 relative to the lower roller 30. The drive mechanism includes a cam member 50 in the form of an inclined plane adapted to be moved horizontally for driving a cam follower 51 vertically. The cam follower 51 is in the form of a Wheel adapted to ride upon the inclined plane of the cam member 50 and to be moved vertically in either direction from the position illustrated in FIG. 3. The cam follower wheel 51 is rotatably mounted in a bracket 52 secured intermediate the ends of a cross brace 53. One end of the brace 53 extends beyond the end plate 25 and is connected to a link 54 which is connected by a pin 55 to the end of the plate 44. Similarly, the other end of the brace 53 is connected to a link 56 which is connected to the plate 45 by a pin 57. Upon movement of the inclined member 50 either to the left or right, as viewed in FIG. 3, the wheel 51 being held against horizontal movement will be moved vertically. Such movement of the cam follower produces corresponding movement of the cross brace 53 thereby moving both ends of the plates 44, 45 simultaneously and causing the roller 31 to move relative to the lower fixed roller 31.

, Actuation of the inclined plate 50 to the left or right as viewed in FIG. 3 is accomplished by means of an air cylinder and piston unit 58 connected by an air tubing 59 to a suitable supply 60 of air pressure. The supply 60 may in turn be connected to the machine logic for controlling movement of the roller 30, 31 into engagement for a fusing operation only at such times that a sheet of support material is in position between the rollers.

The lower roller 30 is driven in the direction illustrated in FIG. 5 by the upper roller 31 during pressure contact therebetween. The shaft 41 for the upper roller 31 has a timing pulley 61 secured thereto and is drivingly connected by a timing belt 62 to the drive system for the machine utilizing the fuser apparatus. When the roller 31 is in pressure contact with the roller 30, motion imparted to the shaft 41 and the roller 31 is imparted to the lower roller 30. As shown in FIG. 6, with the blanket 37 being pliable, the upper roller 31, having a periphery harder than that of the roller 30, when in pressure contact therewith forms a depression 63 of a sufficient arc length to aid in imparting the driving motion to the lower roller. More importantly, the arc length of the depression 63 also provides an extended time and surface that the lower roller 30 has with the toner particles to be fused when a sheet of paper carrying the toner particles is being driven between the rollers.

As previously stated the lower roller 30 serves as the heated roller in the fuser apparatus. A sheet of paper being directed to the nip between the rollers by the conveying system 16 and the guide rods 32 will carry the unfused toner image on its lower surface in direct contact with the release material 38 provided on the lower roller. The lower roller 30 has heat applied thereto externally by means of a quartz lamp 64 mounted in the fuser frame along the length of the lower roller so that its axis is generally parallel thereto. The lamp 64 is surrounded by a reflector 65 which also extends for the length of the lower roller. The lamp 64 is mounted Within the reflector 65 by suitable snap clamps -66 secured each to an adjusting plate 67 adjustably mounted on each of the end plates 25, 26 respectively. The plates 67 may be adjusted relative to their respective end plates in order to position the heat lamp 63 selectively toward or away from the lower roller 30 in accordance with the amount of heat to be imparted to an unfused toner image on a sheet of paper being transported between the rollers.

The reflector 65 may be fabricated into the configuration of a housing having a longitudinal opening nearly closed by the lower roller 30. This serves to aid in retaining the heat generated by the lamp 64 and to apply this heat to a larger area of the roller thereby conserving energy for fusing purposes. In the event that additional heat is necessary for augmenting the heat generated by the lamp 64, the reflector housing is also provided with a ribbon heater 68 which is mounted to be in a heating position relative to the periphery of the lower roller. A suitable heat insulating cover 69 preferably circular in shape and concentric with the axis of the upper roller 31 is mounted on the upper edges of the end plates 25, 26 immediately above the upper roller.

In operation, a sheet or web of support material such as paper is directed into the nip between the rollers 30, 31 in a manner wherein the toner image to be fused is on the lower surface of the horizontally moving transfer material. Radiant heat from the heat lamp 64 is applied to the outer surface of the roller 30.

Fusing is accomplished by the structure so far described by virtue of the principles of low thermal mass. With heat being applied externally by the heat lamp 64 and/or the ribbon heater 67, the blanket 37 serves as a heat barrier to the heat applied externally thereby almost eliminating heat losses due to the roller 30, its supporting shaft 35 and the bearings which support the shaft for rotation in the fuser apparatus. The metallic parts for the lower roller 30 and its supporting structure then do not provide a heat sink for the heat generated upon the surface of the roller. With this arrangement, only a very small amount of heat from the lamp 64 will be needed to maintain the heat balance on the roller 30 in view of the loss of some heat through the rollers supporting structure. This results in the utilization of practically to be moved all of the heat produced by the lamp 64, except for the slight radiation and convective losses, for fusing purposes. In addition, the response time for the heating elements of the fuser (in condition to cause fusing properly) is relatively fast and, for high speed electrostatic copying or duplication, the heat that can be applied to the exterior of the roller will be adequate for high fuser roller speeds. In addition, the warmup period to bring the roller surface to a fusing temperature is extremely short, on the order of two or three minutes with less power needed than for conventional roller fusers. Since there is a minimum loss of heat by way of conduction and radiation, the amount of energy necessary to energize the heating elements may be substantially reduced in comparison to those roller fusers which utilize the an internal heating element generally mounted within the heated roller. With less power requirements for the heating elements, these are capable of longer life cycles and present little or no fire hazard. With practically no heat being applied to the supporting shaft for the rollers, the bearings supporting the same do not experience the usual heat that would be generated from heating elements positioned within the heater roll.

The coating 38 serves to prevent offset of toner particles and, when in a tacky condition during a fusing operation, from adhering to the roller 30 and being brought into contact with the other portions of support material. As previously stated, the amount of heat that the radiant heating lamp 64 must supply is that which is given up to the toner particles and the support material to fuse the particles thereon plus the very small amount of heat that will be lost in being transferred from its point of application to the support material and to maintain the heat balance caused by the minimal losses through the supporting structure for the fuser rollers. This may be very precisely controlled to insure a minimum loss of heat. The use of low thermal mass concept for fusing configuration also assists in the prevention of toner olfset in that this temperature may be more precisely controlled.

While the invention has been described with reference to the strutcure disclosed herein it is not confined to the details set forth and this application is intended to cover such modification or changes as may come with the purpose of the improvements.

What is claimed is:

1. A contact heat fusing apparatus of the type having two fusing members each mounted for movement in an endless path and arranged in contact and adapted to receive and move a support material carrying thermoplastic particles in image configuration for fixing the image, the improvement comprising a thin heat insulating material associated with one of said fusing members and adapted as a barrier against the inward flow of heat,

and means for applying heat to the exterior of said heat insulating material at a point prior to its contact with particles to be fused during rotation of said one fusing member, the heated exterior being of sufficient temperature for tackifying and fixing the image upon the support material.

2. A contact heat fusing apparatus for fixing thermoplastic particles carried on a support material in image configuration, said apparatus including a support,

a first fusing member mounted for movement in an endless path on said support,

a second fusing member mounted for movement in an endless path on said support and positionable in contact with said first member, said members when in contact arranged to move support material therebetween with the image to-be-fixed in contact with one of the members,

said one member being former therearound with a thin heat insulating material adapted as a barrier against the inward flow of heat,

and means for applying heat to the exterior of said heat insulating material at a point prior to its contact with particles to be fused during movement of said one member, the heat exterior being of sulficient temperature for tackifying and fixing the image upon the support material.

3. The apparatus of claim'2 wherein the other fusing member includes a layer of an insulating material for minimizing the flow of heat therethrough during a fusing operation.

4. The apparatus of claim 2 wherein said means for applying heat is an elongated radiant heater element arranged along ands-paced from the exterior of the material and adapted to effect the radiation of heat to said exteriorp References Cited UNITED STATES PATENTS 3,21979'4 11/1965 Mindell et al. 219-388 lCHN J. CAMBY, Primary Examiner US. Cl. X.R. 219-388 

